Re: [Qemu-devel] [PATCH for 2.13 1/2] Revert "spapr: Don't allow memory hotplug to memory less nodes"

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Thu, Apr 05, 2018 at 10:35:22AM -0400, Serhii Popovych wrote:
> This reverts commit b556854bd8524c26b8be98ab1bfdf0826831e793.
> 
> Leave change @node type from uint32_t to to int from reverted commit
> because node < 0 is always false.
> 
> Signed-off-by: Serhii Popovych <spopovyc@redhat.com>
> ---
>  hw/ppc/spapr.c | 22 ----------------------
>  1 file changed, 22 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 2c0be8c..3ad4545 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3477,28 +3477,6 @@ static void spapr_machine_device_plug(HotplugHandler *hotplug_dev,
>              return;
>          }
> 
> -        /*
> -         * Currently PowerPC kernel doesn't allow hot-adding memory to
> -         * memory-less node, but instead will silently add the memory
> -         * to the first node that has some memory. This causes two
> -         * unexpected behaviours for the user.
> -         *
> -         * - Memory gets hotplugged to a different node than what the user
> -         *   specified.
> -         * - Since pc-dimm subsystem in QEMU still thinks that memory belongs
> -         *   to memory-less node, a reboot will set things accordingly
> -         *   and the previously hotplugged memory now ends in the right node.
> -         *   This appears as if some memory moved from one node to another.
> -         *
> -         * So until kernel starts supporting memory hotplug to memory-less
> -         * nodes, just prevent such attempts upfront in QEMU.
> -         */
> -        if (nb_numa_nodes && !numa_info[node].node_mem) {
> -            error_setg(errp, "Can't hotplug memory to memory-less node %d",
> -                       node);
> -            return;
> -        }
> -

If you remove this unconditionally, wouldn't it be a problem in case
of newer QEMU with older guest kernels ?

Regards,
Bharata.